First, you will nee to store the original form values in session variables.
on the second page, go to the bindings panel, click the plus button and select From Data. Click the folder icon and select the first form page.
this will add a bindings group to the second page for the form elements on the first page.
On the server behaviors panel, click the plus button and select WebAssist -> eCart -> General -> Set Session value.
For the trigger, click the lightning bolt icon and expand the binding group for the form from the first page and select the submit button form that form.
For the value, click he lightning bolt icon and expand the binding group for the form from the first page and select the first form element, set the name of the session to the same name as the form element.
repeat this for each form element.
for the back button, use a standard button type and an href link around it:
<a href="formular_page1.php"><input name="FormularPage1" type="button" id="button" value="FormularPage1"></a>
Now ont he first page, set the value or each form element to use the corresponding session binding